(First Related Art)
An example of the method for producing a silicon single crystal from polycrystalline silicon is a Czochralski process (hereinafter referred to as a CZ process). Generally, a single crystal pulling apparatus used for the CZ process comprises a quartz crucible for accommodating silicon melt, a graphite crucible for retaining the quartz crucible, a tray for securing and holding the graphite crucible from below, a crucible rotating shaft supporting the tray from below and elevating and lowering the tray and the crucibles while rotating the tray and the crucibles, and a heater disposed around the outer periphery of the graphite crucible, for example. The graphite crucible and the quartz crucible are heated by the heater, whereby silicon is melted.
Since the crucible, the tray and the crucible rotating shaft are all commonly made of graphite in such a single crystal pulling apparatus, the following problems arise. The graphite material has high thermal conductivity. For this reason, the heat inside the crucible is conducted from the tray to the crucible rotating shaft. Consequently, the heat escapes out of the furnace. In other words, the heat quantity provided for melting a metal is conducted through the graphite material and escapes, and therefore, heat loss occurs. This results in a decrease in the temperature inside the crucible, and in order to compensate the heat loss, additional heating corresponding to the loss is necessary. Consequently, the problem of additional electric power consumption arises. Another problem is as follows. When the quantity of heat escape from the crucible bottom portion is great, the temperature of the melted material (such as silicon and germanium) in the quartz crucible bottom portion drops, so convection of the melted material occurs because of the temperature difference between the melted material in the quartz crucible bottom portion and that in the crucible upper portion. Such convection is extremely detrimental to the single crystal pulling apparatus, which prevents a stable pulling process.
In order to solve such problems, it has been proposed to interpose and arrange a low heat conductive member for suppressing heat conduction in a shaft direction in the crucible rotating shaft (see the following Patent Document 1). Patent Document 1 also proposes, for example, that the low heat conductive member is formed of a carbon fiber-reinforced carbon composite material and that the entire crucible rotating shaft is formed of a carbon fiber-reinforced carbon composite material.
(Second Related Art)
An example of the method for producing a silicon single crystal from polycrystalline silicon is a Czochralski process (hereinafter referred to as a CZ process). Generally, a single crystal pulling apparatus used for the CZ process comprises, as shown in FIG. 10, a quartz crucible 50 for accommodating silicon melt, a graphite crucible 51 for retaining the quartz crucible 50, a crucible rotating shaft 52 for elevating and lowering the graphite crucible 51 and the quartz crucible 50, and a heater 53 disposed around the outer periphery of the graphite crucible 51, for example. Note that reference numeral 54 indicates a heat shielding member, reference numerals 55 and 56 indicate gas exhaust passages for, for example, SiO gas, and reference numeral 57 indicates a gas exhaust port.